The overall objective of the research is to determine neuroendocrine mechanisms governing sexual maturation. The domestic sheep will be used as the animal model. The proposed research will extend our working hypothesis on control of the timing of puberty through an increase in frequency of LH pulses. Studies will be conducted to address fundamental issues in regulation of LH secretion by steroid negative feedback, by steroid-independent control, by endogenous opioids and by melatonin. Artificial light treatments will be used extensively to probe the developing neuroendocrine system in order to ascertain the ontogeny of the endogenous melatonin rhythm and its link to the system controlling LH secretion. Measurement of other circadian rhythms by a telemetric system during the early postnatal period will facilitate understanding why the pineal gland of the neonatal lamb does not produce a pattern of melatonin that accords with the prevailing photoperiod. The light requirements for puberty will be studied; lambs, rendered nonphotoperiodic by denervation of the pineal gland, will be exposed to a brief duration (5 weeks) of molatonin treatment to test the hypothesis that one photoperiod has initiated a sequence of events that lead to puberty, puberty can occur in the absence of any prevailing light signals. Moreover, studies will be conducted that bear upon the concepts that an adult seasonal breeder undergoes an "annual puberty" and that the circannual rhythm of reproduction is innate, rather than established through experience. An investigation will be carried out to determine if the functioning of the system regulating steroid-feedback sensitivity can be separated from that controlling steroid-independent modulation of LH secretion. The involvement of endogenous opioids in the regulation of LH pulse frequency will be examined in the context of photoperiod-induced changes in sensitivity to estradiol feedback inhibition. The research has broad application to the understanding of how puberty is timed in animals, knowledge that will ultimately contribute to greater understanding of normal and delayed puberty in children.